Container base



FIG. 1 is a top perspective view of a container base showing our new design;

FIG. 2 is a top view thereof;

FIG. 3 is a side view thereof;

FIG. 4 is another side view thereof; and,

FIG. 5 is a bottom view thereof.

The broken lines in the figures depict portions of the container base that form no part of the claimed design. 

CLAIM The ornamental design for a container base, as shown and described. 